Synthesis and characterization of graft and block copolymers using hydroboration

Graft and block copolymers were synthesized using multifunctional and
monofunctional macroinitiators to produce the copolymers. The process involved
hydroboration of commercially available unsaturated rubbers and chain-end
unsaturated macromonomers with 9-borabicyclo [3.3.1] nonane (9-BBN). The
resulting secondary alkyl 9-BBN moieties in the starting materials were subsequently
exposed to oxygen in the presence of free radical polymerizable monomers to
facilitate the formation of graft and block copolymers.
This research was initiated by first studying the hydroboration of a model compound,
2-hexene, in order to determine the optimal conditions for the graft reactions. The
model compound was subsequently used as a macroinitiator to initiate the
polymerization of methylmethacrylate (MMA). The same borane chemistry was
extended to the synthesis of polystyrene (PS) block copolymers. Chain-end
unsaturated PS macromonomers, synthesized by anionic polymerization, were
effectively hydroborated and then polymerized to produce PS-b-PMMA block
copolymers.
The synthesis of polyolefin graft copolymers was subsequently achieved by
hydroboration. Several commercial rubbers with different levels of unsaturated
segments were efficiently grafted with vinyl monomers MMA and styrene (St)
following the “graft from” approach. The grafted reactions were carried out under
various reaction conditions to determine the effect of the following factors:
concentration of oxygen, amount of borane and monomer concentration. By
controlling these factors, different graft densities were achieved with high graft
efficiencies. All reactions produced mixed products including unreacted
(non-functional) macroinitiator, homopolymer, graft copolymer and in case of the
highly unsaturated polymer a crosslinked gel.
Finally, the chemical compositions as well as the molar mass distribution of the graft
copolymers were fully characterized by different chromatographic techniques.
1H-NMR and FTIR were also used to confirm the structure of these copolymers.
Gradient HPLC was developed and extensively used to characterize the graft
copolymers.